This invention relates to a weigher-conveyor system for weighing an object while this object is being transported by a conveyor belt.
It has been known to use a weigher-conveyor system for automatically measuring or checking the weight of an object being transported. Such a weigher-conveyor system is generally comprised of a weighing device supporting a conveyor with a belt stretched between a pair of rollers such that both the weight of an object which is received thereby from a feeder conveyor on its upstream end and the weight of the conveyor itself will be applied to the weighing device. Since the weight of the conveyor is a constant, the weight of the object can be obtained from this total load on the weighing device.
Weighing methods by using a weigher-conveyor system of this kind may be roughly divided into the dynamic weighing whereby the weight of an object is measured while it is being transported and the static weighing whereby the conveyor is momentarily stopped while the object is weighed. Advantages and disadvantages of these two types may be summarized as shown in Table 1.
TABLE 1 ______________________________________ Dynamic Weighing Static Weighing ______________________________________ Accuracy Low High Wheel Balancing High Precision Unnecessary Weighing Capability Fast Slow Limitation on Size Severe Limitation OK up to length of Target Object of conveyor ______________________________________
Since the dynamic and static weighing methods have mutually opposite functional characteristics, as can be ascertained from Table 1, there have been attempts to make both options available and selectively using one of them, depending on the kind of objects to be weighed. In this situation, however, there arises the new problem of how to choose one or the other of these two methods for target objects having different dimensional and weight characteristics. As a result, the advantages of the individual methods are often not utilized fully, and there remained the problem of not being able to speedily process objects with different dimensions and weights.